Nozbe - a to-do, task manager focused on GTD…every task to assigned to a project and also to a context…see more. Others I’ve covered are Gubb, workhack, and Imified…Remember The Milk always gets a mention.
Vitalist - similar to Nozbe (above), but more features.
Izimi - Tubes and dekoh are services that enable file sharing from your desktop.
Izimi is the latest to this bunch, basically you are sharing the files on your desktop without having to upload stuff to a storage service, it’s more an access than a storage perspective, it also doubles up as a social network.
Lingr - tag based chat rooms, find rooms by tag, and join the chat. Keep track of new chat rooms via RSS feeds, also keep up on a chat via an RSS feed or tray pop-ups. Promote a badge that links straight to a chat room.